Fix warning message

Author: gaearon

packages/react-test-renderer/src/ReactTestHostConfig.js

@@ -67,7 +67,7 @@ export function appendChild(
     warning(
       Array.isArray(parentInstance.children),
       'An invalid container has been provided. ' +
-        'This may indicate that another render is being used in addition to the test renderer. ' +
+        'This may indicate that another renderer is being used in addition to the test renderer. ' +
         '(For example, ReactDOM.createPortal inside of a ReactTestRenderer tree.) ' +
         'This is not supported.',
     );